graeme uk,
Not sure how long the battery will last but, have been using it for at least a dozen plus hours and no sign of stopping. The basic circuit setup - opamp, feedback with rail splitter is similar enough to an opamp based headphone amp, with the exception of RIAA, that would expect that battery life is pretty good. I have made several CMoy type headphone amplifiers and battery life is typically not a problem.
Cheers -ALBQ

Okay, I have "assembled a total of 3 units, troubleshooting each, resoldering, dismantling, etc. The best I have now is low volume in one channel (right) and dead left channel. Ordinarily, I would keep going. But, this is way too hard for a neophyte like me. The fun is fast departing. Any ideas? I used the Tangent tutorial to the letter

Bob,
Couple of questions 1) are you using the original schematic? 2) could you post a picture of your build? I have built a couple of these now and all work fine. If you could provide a picture or two and some infomration, I will try to help.
Thank you -ALBQ

Bob,
Hmmm... Hard to tell whats going on from the pic. At a glance, generally looks like I would suspect - very similar to a CMoy headphone amp layout. Do you have a voltmeter? The first thing to check are the +/- rails on the opamp - should read +/-4.5V from virtual ground. Let me know if this is correct and will move to the next step.
Thank you -ALBQ

Bob,
If you measure -4.5V (PIN4) and +4.5V (PIN8), would ask what IC you are using? All of the Burr Brown / Anolog Devices dual opamps are the same pin out so, if the rails are corrct, would need to be something else wrong. Most likely in the feeback loop. What are the voltages at each pin of the opamp?
Thank you -ALBQ

I'm using BB/TI opamp. I'll have to consult my basic electronics book for measuring pins of the opamp, unless it just requires a positive reading per leg against a common negative. I just rechecked my test pins and now I can hear the source very faintly in BOTH channels! When I unplug the 9 volt, no change on the audible output. It's as if the amp is doing nothing but allowing a "pass through" signal with no amplification.